1. Field of the Invention
The present invention relates generally to methods of controlling air fuel ratio learning for dual injection internal combustion engines in hybrid vehicles, and particularly to those for dual injection internal combustion engines including an injector injecting fuel into a cylinder for in-cylinder injection and an injector injecting fuel into an intake manifold or port for in-intake air path injection, and dual injection internal combustion engines mounted on hybrid vehicles and driven by assistive dynamic
2. Description of the Background Art
A known hybrid vehicle is driven by an internal combustion engine and an electric motor or similar assistive dynamic.
Furthermore, a so-called dual injection internal combustion engine is also known. More specifically, it includes an injector injecting fuel into a cylinder for in-cylinder injection and an injector injecting fuel into an intake manifold or port for in-intake air path injection and in accordance with the engine's running condition the injectors are switched for example to achieve stratified combustion for a low load driving range and homogenous combustion for a high load driving range and in accordance with a driving condition a predetermined share ratio is applied to inject the fuel for example to achieve improved fuel efficiency and output characteristics.
Furthermore, an internal combustion engine has its output, exhaust and other characteristics and, furthermore, its drivability and other similar variety of performance corrected by controlling an air fuel ratio of an air fuel mixture supplied to the engine by correcting the ratio through feedback to be a target air fuel ratio matching a driving condition of interest. To provide the control through feedback for correction with increased precision, learning of an air fuel ratio learning value, or air fuel ratio learning, is controlled and this value is reflected in the control through feedback for correction.
If an air fuel ratio is collected through feedback and thus controlled and air fuel ratio learning is controlled, as described above, in an internal combustion engine mounted in a hybrid vehicle, a problem arises: a type of hybrid vehicle has its internal combustion engine stopped depending on the vehicle's running condition, when air fuel ratio learning will not be controlled. As a result, the air fuel ratio learning control is not completed at an early stage as expected and accurate air fuel ratio feedback correction control may not be exerted. Japanese Patent Laying-Open No. 2000-291471 addresses such disadvantage. More specifically, an air fuel ratio learning value is learned in a learning area divided into a plurality of subareas corresponding to driving conditions and for at least one subarea the value is learned in a vicinity of the center of the subarea, and to do so a ratio of requested output to an internal combustion engine and assistive dynamics is determined and feedback operation is also compulsorily performed to complete the air fuel ratio learning control at an early stage.
The technique described in Japanese Patent Laying-Open No. 2000-291471 is, however, associated with an internal combustion engine including only a single injector, and does not allow for a dual injection internal combustion engine including an injector injecting fuel into a cylinder for in-cylinder injection and that injecting fuel into an intake manifold or port for in-intake air path injection. If air fuel ratio learning control is completed at an early stage for only one injector, i.e., the control is not completed for both injectors, it is difficult to learn which injector injects an amount of fuel contributing to air fuel ratio variation. Thus for dual injection internal combustion engine there is a demand for early and in addition accurately controlling air fuel ratio learning for each of both injectors.